Acoustic dry partitions: acoustic plasterboard and high-density gypsum
Regulatory framework applicable to commercial offices: four sound insulation targets ranging from 28 to 45 dB.
+4 dB of sound insulation gain for a 15% material cost premium – the best performance-to-thickness ratio on the commercial market: acoustic plasterboard on a 72/48 frame delivers Rw 38 dB at 72 mm, whereas an equivalent masonry solution requires 150 to 200 mm. For architects weighing leasable m² against partitioning layout, the difference is decisive. The commercial acoustic standard sets four sound insulation targets between rooms (28, 32, 38, 45 dB), and acoustic plasterboard systems (Placo Phonique by Saint-Gobain, Siniat Pregyplac dB, Knauf KA13 Phonik) cover this entire range in 72/48 and 98/48 configurations. Kytom has deployed these systems since 2006 on floor plates delivered in 12 weeks on average, compliant with the DTU.
The NF S 31-080 standard structures the acoustic comfort of French commercial spaces around four sound insulation thresholds between rooms:
- 28 dB: meeting room with limited confidentiality.
- 32 dB: standard shared office.
- 38 dB: executive office (directional target).
- 45 dB: confidential room (legal, human resources, medical).
Partition performance is measured in the laboratory via the Rw index, and installation follows the DTU. Acoustic plasterboards (13 mm, 1.2 x 2.5 m or 1.2 x 2.7 m format) feature a high-density gypsum core, about 30% heavier than a standard board, which dampens vibrations transmitted through the wall.
Noise is the leading source of reported discomfort in commercial open spaces. The target ambient noise aims for 35-40 dB(A) in an open-plan floor and 30-35 dB(A) in a closed office, in line with the NF S 31-080 framework. A complementary standard published in 2016 specifies the arrangement applicable to collaborative spaces.
For the architect: 4 acoustic plasterboard configurations calibrated from Rw 38 to Rw 55 dB and their impact on the layout
The choice of configuration is not just acoustic: it sizes the partitioning layout, and therefore the usable area / leasable area ratio that the architect presents to the client. Moving from 72 to 120 mm of thickness over 200 linear metres of partitions consumes nearly 10 m² of floor area, representing a significant amount of avoided rent in a dense commercial zone. Four standard configurations cover the bulk of commercial cases:
| Configuration | Composition | Rw (dB) | Thickness | Target use |
|---|---|---|---|---|
| 72/48 single layer | Acoustic plasterboard 1 side + 45 mm insulation | 38 | 72 mm | Executive office |
| 98/48 double layer | 2× acoustic plasterboard each side + 45 mm insulation | 50 | 98 mm | Confidential room |
| 120/70 reinforced double layer | 2× acoustic plasterboard + 70 mm insulation + absorbent facing | 55 | 120 mm | Boardroom |
| Fire-rated variant | Type F or DF boards + reinforced frame | 38-50 | 72-120 mm | EI 30 to EI 60 |
Rw values taken from standard manufacturer data sheets for 2023 acoustic boards, based on standardised weighted sound reduction index tests.
Our reading differs from common practice on one point: the 98/48 double layer is not justified everywhere the brief lists « confidential room ». In practice, a significant proportion of rooms thus labelled in specifications actually correspond to meeting rooms with limited confidentiality (28 to 32 dB target), over-specified by drafting habit. The real-use trade-off, conducted with the client during the detailed design phase, frequently allows a switch to 72/48 and the recovery of 26 mm of thickness per partition.
Installation follows the DTU: laser tracing, screwed metal frame, non-compressed fibrous insulation, cross-laid boards with staggered joints, perimeter sealing strips, joint treatment in 3 passes. The average execution time runs to 12 weeks for an 850 m² floor plate.
When acoustic plasterboard is not the right answer. Below the required Rw 32 dB (circulation spaces, rooms not permanently occupied), the standard 13 mm board on a 48 mm frame is sufficient: the cost premium of high-density gypsum is not justified. Conversely, above the targeted Rw 55 dB (audio studios, instrumented medical rooms, trading floors), the dry partition reaches its physical limit: you must switch to a decoupled double partition with an air gap, or even 200 mm concrete masonry, otherwise the thickness exceeds 150 mm for a marginal gain. For reconfigurations more than 4 times over 10 years, the demountable partition becomes more cost-effective again than the dry partition rebuilt at each cycle.
Measured benefits: 4 dB of gain and 50% less perceived sound discomfort
The acoustic plasterboard provides a documented gain of 4 dB compared to a standard board of the same thickness, measured by standardised sound reduction tests. As human auditory perception is logarithmic, a 4 dB difference corresponds to a reduction of about 50% in the sound discomfort perceived by the ear (standard psychoacoustic law).
From the field feedback accumulated since our founding, three observations recur:
- The 98/48 double layer Rw 50 dB configuration meets the 45 dB confidential target with a 5 dB margin that absorbs lateral transmissions through floors, ceilings and joinery.
- Executive offices fitted in 72/48 Rw 38 dB reach the directional target without the cost of additional insulation.
- A noticeable reduction in ambient noise improves concentration and limits cognitive fatigue at the end of the day, an effect documented by research in acoustic ergonomics. This observation aligns with the trend seen for sound discomfort in open spaces.
The performance-to-thickness ratio remains favourable: 72 mm of acoustic plasterboard partition for 38 dB of reduction, versus 150 to 200 mm for an equivalent masonry solution (typical order of magnitude for plaster brick solutions). Environmental certification and usage quality standards reward these insulation levels in their acoustic comfort credits.
Limits to anticipate: DnT,A site -5 dB, sound bridges and weak links at door / glazing
The Rw index stated by manufacturers results from laboratory tests. The actual on-site insulation measured (DnT,A indicator) generally remains 3 to 5 dB below the laboratory values, due to lateral transmissions through floors, ceilings, technical ducts and perimeter joinery. Sealing and the treatment of penetrations determine the final delivered performance.
Four points of vigilance shape the quality of the result:
- Vertical continuity: the partition must return to the structural ceiling slab, mandatory for Rw 45 and 50 dB targets; stopping at the suspended ceiling significantly degrades the DnT,A measured at handover.
- Door weak link: an Rw 32 dB acoustic door on an Rw 50 dB partition caps the overall insulation at 35-37 dB according to the acoustic composition law.
- Technical sound bridges: facing electrical sockets, traversing mechanical ventilation ducts and unsealed boxes nullify a significant portion of the wall’s performance.
To treat reverberation at floor level, see our office acoustic correction.
